1. Field of the Invention
This invention relates to an assembly of shield casings stacked in a direction of height, and more particularly to a plurality of shield casings having an intermediate flat plate disposed there between.
2. Related Art
Heretofore, as shown in FIG. 3, in an antenna unit 1 first and second shield casings 61 and 62 are provided between an antenna cover 2 and a base 3 in such a manner that those casings 61 and 62 are stacked in the direction of height thereof. The first shield casing 61 accommodates a GPS antenna section for receiving signals from a GPS satellite. The GPS antenna section comprises a patch antenna, a signal receiving circuit, an RF converter. The second shield casing 62 accommodates a tuner section which comprises an FM tuner section, a digital demodulator section, and a connector.
The first and second shield casings 61 and 62 are made of a metal sheet, and are equal and rectangular in cross section. The top surface and the bottom surface of the first shield casing 61 are covered with a top surface shield cover 71 and a bottom surface shield cover 72 which are both made of a metal plate. Similarly, the top surface and the bottom surface of the second shield casing 62 are covered with a top surface shield cover 73 and a bottom surface shield cover 74 which are both made of a metal plate.
The shield covers 71, 72, 73 and 74 are made up of: flat plates 71A, 72A, 73A and 74A which covers the top surfaces and the bottom surfaces of the two shield casings 61 and 62; and several side surface retaining springs 80 which press against the side walls of the shield casings 61 and 62. The retaining springs 80 are extended from the outer edges of the flat plates 71A, 72A, 73A and 74A, and are bent upwardly or downwardly depending on the positions of the flat plates 71A through 74A.
The retaining springs 80 have holes 85 as shown in FIG. 4, while side walls (four side walls) of the first and second shield casings 61 and 62 have protrusions 65 which are engaged with the aforementioned holes 85.
The above-described antenna unit 1 is assembled as follows: First, the GPS antenna section is built in the first shield casing 61, and then shield casing 61 is covered with the top surface shield cover 71 and the bottom surface shield cover 72. Next, the tuner section is built in the second shield casing 62, and the latter 62 is covered with the top surface shield cover 73 and the bottom surface shield cover 74. Thereafter, the first shield casing 61 with the shield covers 71 and 72 is mounted on the second shield casing 62 with the shield covers 73 and 74 through an insulating sheet 90, and the first and second shield casings 61 and 62 are secured to each other with suitable means.
As was described above, heretofore in the case where the first and second shield casings 61 and 62 which are polygonal and substantially equal in cross section are stacked in the direction of height thereof, the following method is employed: The first and second shield casings 61 and 62 are assembled separately, and in the final assembling step the shield casing 61 is mounted on the second shield casing 62. Hence, the shield casings 61 and 62 need four shield covers 71 through 74, two shield covers for each shield casing. Additionally, it is essential to place the insulating sheet between the first and second shield casings 61 and 62, and therefore the resultant antenna unit is relatively high in manufacturing cost. Furthermore, the first and second shield casings 61 and 62 thus stacked must be fixedly positioned. That is, it is rather troublesome to assemble the conventional antenna unit.